Catalyst compositions similar to those of the invention are disclosed in Belgian Pat. No. 773,851 which discloses catalysts of the composition molybdenum, vanadium, tungsten and antimony and one or more of the oxides of lead, silver, tin, titanium, copper and bismuth. U.S. Pat. No. 3,736,354 discloses the catalyst compositions containing the oxides of vanadium, molybdenum and germanium and the oxides of vanadium, molybdenum and copper. German Pat. No. 2,414,797 discloses a catalyst for the production of acrylic and methacrylic acids from acrolein or methacrolein which contains the metal oxides of molybdenum, vanadium, copper and at least one element of the group of iron, cobalt, nickel and magnesium. U.S. Pat. No. 3,725,472 discloses a catalyst for the oxidation .alpha..beta.-unsaturated carbonylic compounds to the corresponding unsaturated acids employing a catalyst containing the oxides of molybdenum, vanadium and antimony.
None of the foregoing patents, however, disclose the catalyst compositions of the present invention wherein unexpectedly high yields of unsaturated carboxylic acids are obtained from the corresponding unsaturated aldehydes in the presence of these catalysts.